diff --git a/src/iso.c b/src/iso.c
index cd1cb2c1..1e809014 100644
--- a/src/iso.c
+++ b/src/iso.c
@@ -631,7 +631,7 @@ static void update_md5sum(void)
 	free(md5_data);
 }
 
-// Returns 0 on success, nonzero on error
+// Returns 0 on success, >0 on error, <0 to ignore current dir
 static int iso_extract_files(iso9660_t* p_iso, const char *psz_path)
 {
 	HANDLE file_handle = NULL;
@@ -668,9 +668,20 @@ static int iso_extract_files(iso9660_t* p_iso, const char *psz_path)
 	_CDIO_LIST_FOREACH(p_entnode, p_entlist) {
 		if (FormatStatus) goto out;
 		p_statbuf = (iso9660_stat_t*) _cdio_list_node_data(p_entnode);
-		if ((p_statbuf->rr.b3_rock == yep) && enable_rockridge) {
-			if (p_statbuf->rr.u_su_fields & ISO_ROCK_SUF_PL)
+		if (scan_only && (p_statbuf->rr.b3_rock == yep) && enable_rockridge) {
+			if (p_statbuf->rr.u_su_fields & ISO_ROCK_SUF_PL) {
 				img_report.has_deep_directories = TRUE;
+				// Due to the nature of the parsing of Rock Ridge deep directories
+				// which requires performing a *very costly* search of the whole
+				// ISO9660 file system to find the matching LSN, ISOs with loads of
+				// deep directory entries (e.g. OPNsense) are very slow to parse...
+				// To speed up the scan process, and since we expect deep directory
+				// entries to appear below anything we care for, we cut things
+				// short by telling the parent not to bother any further once we
+				// find that we are dealing with a deep directory.
+				r = -1;
+				goto out;
+			}
 		}
 		// Eliminate . and .. entries
 		if ( (strcmp(p_statbuf->filename, ".") == 0)
@@ -702,15 +713,18 @@ static int iso_extract_files(iso9660_t* p_iso, const char *psz_path)
 				}
 				safe_free(psz_sanpath);
 			}
-			if (iso_extract_files(p_iso, psz_iso_name))
+			r = iso_extract_files(p_iso, psz_iso_name);
+			if (r > 0)
 				goto out;
+			if (r < 0)	// Stop processing current dir
+				break;
 		} else {
 			file_length = p_statbuf->total_size;
 			if (check_iso_props(psz_path, file_length, psz_basename, psz_fullpath, &props)) {
 				continue;
 			}
 			print_extracted_file(psz_fullpath, file_length);
-			for (i=0; i<NB_OLD_C32; i++) {
+			for (i = 0; i < NB_OLD_C32; i++) {
 				if (props.is_old_c32[i] && use_own_c32[i]) {
 					static_sprintf(tmp, "%s/syslinux-%s/%s", FILES_DIR, embedded_sl_version_str[0], old_c32_name[i]);
 					if (CopyFileU(tmp, psz_fullpath, FALSE)) {
diff --git a/src/rufus.rc b/src/rufus.rc
index 2bffc811..7817b975 100644
--- a/src/rufus.rc
+++ b/src/rufus.rc
@@ -33,7 +33,7 @@ LANGUAGE LANG_NEUTRAL, SUBLANG_NEUTRAL
 IDD_DIALOG DIALOGEX 12, 12, 232, 326
 STYLE DS_SETFONT | DS_MODALFRAME | DS_CENTER | WS_MINIMIZEBOX | WS_POPUP | WS_CAPTION | WS_SYSMENU
 EXSTYLE WS_EX_ACCEPTFILES
-CAPTION "Rufus 3.12.1687"
+CAPTION "Rufus 3.12.1688"
 FONT 9, "Segoe UI Symbol", 400, 0, 0x0
 BEGIN
     LTEXT           "Drive Properties",IDS_DRIVE_PROPERTIES_TXT,8,6,53,12,NOT WS_GROUP
@@ -397,8 +397,8 @@ END
 //
 
 VS_VERSION_INFO VERSIONINFO
- FILEVERSION 3,12,1687,0
- PRODUCTVERSION 3,12,1687,0
+ FILEVERSION 3,12,1688,0
+ PRODUCTVERSION 3,12,1688,0
  FILEFLAGSMASK 0x3fL
 #ifdef _DEBUG
  FILEFLAGS 0x1L
@@ -416,13 +416,13 @@ BEGIN
             VALUE "Comments", "https://rufus.ie"
             VALUE "CompanyName", "Akeo Consulting"
             VALUE "FileDescription", "Rufus"
-            VALUE "FileVersion", "3.12.1687"
+            VALUE "FileVersion", "3.12.1688"
             VALUE "InternalName", "Rufus"
             VALUE "LegalCopyright", "© 2011-2020 Pete Batard (GPL v3)"
             VALUE "LegalTrademarks", "https://www.gnu.org/licenses/gpl-3.0.html"
             VALUE "OriginalFilename", "rufus-3.12.exe"
             VALUE "ProductName", "Rufus"
-            VALUE "ProductVersion", "3.12.1687"
+            VALUE "ProductVersion", "3.12.1688"
         END
     END
     BLOCK "VarFileInfo"